Page - 265 - in Loss and Damage from Climate Change - Concepts, Methods and Policy Options

11 TheRoleof thePhysicalSciences inLossandDamage… 265 To evaluate the current and changing likelihood of climatic hazards different sourcesofinformationareemployed(IPCC2012,2013,2014a,b).Historicalrecords of climate variables, such as temperature or precipitation, are used to estimate the hazard probability under historical climatic conditions. Climate models are used to estimate changes of these variables in the future under different scenarios of greenhousegasses’emissionsorconcentrations.Hazardandimpactmodelsare then employed to evaluate how changes in climatic variables will produce changes in natural or human systems, e.g., how changes in precipitation patterns will affect flood regimes inagivencatchment. In the restof this sectionwebrieflydescribe the informationand toolsutilised to estimate thecurrentobservedhazardprobabilityand itsprojectedchanges. 11.2.1 ObservedHazard Historical records of climate variables must be accurate, representative, homoge- neous and of sufficient length if they are to provide robust estimates of current hazardprobability.Therobustnessof the inferredprobabilitiesdepends for instance on the record length; short records of precipitation in a particular location do not provide enough informationabout the extremeprecipitation events thatmight have occurred in the past. Poor quality of data (incorrect records or missing data) can induce largeuncertainties in the estimationof current climatic hazards.While data for temperature and precipitation ismorewidely available, other variables such as soilmoisturearepoorlymonitored, or extremewindspeedsarenotmonitoredwith sufficient spatial resolution. Paleoclimatology can provide information about rare, large magnitude hydro- meteorological events in places where long enough observational records are not availableandgoodproxies toestimatethemagnitudeofpasteventssuchasfloodsor droughtscanbefound.For instance, instrumental recordsoffloodsatgaugestations are limited inspatial coverageand time,withonlyasmallnumberofgaugestations spanningmorethan50years.Pre-instrumentalflooddatacanprovideinformationfor longerperiods, however thecurrent availabilityof this data is scarceparticularly in spatialcoverage(IPCC2012).Paleoclimatedatacanthenprovideinformationabout a range of climate hazards that have occurred in the remote past, often illustrating the fact that, inmany cases, the recent observational records provide very limited informationabouttherangeoftheunforcednaturalvariabilityinaparticularlocation (Benitoetal.2004;IPCC2012).However,paleoclimatologycanonlyprovideinfor- mation in caseswhere adequate proxies exist, as for instance tree-ring temperature and rainfall reconstructions, paleo coastal surges, etc.; but it is not a viable option for someothervariables suchashigh resolutionwindspeed.